The application of optical topography measurement technology is increasing with the rapid development of science and technology, and more applications are developed in different industries. For example, the technology can be used for preliminary identification of defects in the semiconductor industry, and the accuracy of the micro-structure of the surface also affects the effectiveness of the product. The technology can be also used for detecting the contour surface of biological cells, or used as an endoscope to observe the situation in the human body. The technology can be also used for identifying the outer shape of a fuselage, wings, and propeller in the aerospace industry.
The traditional technologies of topographical measurement can be divided into a contact technology and a non-contact technology. The measurement of the contact technology is that an object is scanned by a probe with a high accuracy measurement. The probe contacts with the surface of the object directly in the measurement, and the surface of the object or the probe could be damaged. In measurements using the non-contact technology, such as Maike Sen interferometer, stereoscopic method (dual-view, multi-view) and Near-field scanning optical microscope with Confocal Microscopy, can be also used for detecting objects curvature, shape, and roughness without contacting with the surface of the object, and the surface of the object could not be damaged.
However, there are some defects in the structured light projection technology, fringe projection technology, and other interferences. The structured light projection technology and the fringe projection technology are suitable for detecting the objects with diffusing effect. For a specular object, only the light reflected from some part of the surface can be projected onto the image capturing device to form an image, but the light reflected from the other parts of the surface cannot be projected to form the image, thus the data of a part of the image is lost. Furthermore, the strength of the reflected light projected onto the image capturing device is generally excessive, so that the gray value of the image approaches saturation, and the fringe image is too bright and the contrast is poor.
On the other hand, the measurement technology of the specular objects is based on interference, such as a Michelson interferometer, or a Mach-zehnder interferometer. The measurements need to be executed in a stable environment, such as with low noise or no movement, and is limited by the interference range of the interferometer. Thus the measurement is inconvenient for measuring large objects or specular objects with a discontinuous surface.
As a result, it is necessary to provide a topographical measurement system for a specular object to solve the problems existing in the conventional technologies, as described above.